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States of matter - Gaseous state

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A quick recap on gases !!!

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States of matter - Gaseous state

  2. 2. TYPES Basically we observe with 3 states of matter namely  SOLIDS  LIQUIDS &  GASES
  3. 3. LET’S See …
  4. 4. Apart from the 3 states of matter, there are 2 more states of matter  Plasma  Bohr-Einstein Condensate Plasma is not a common state of matter on the earth , but a common one among stars which produces that excessive heat & light.That means plasma matter has high kinetic energies.
  5. 5. In contrast to this , Bohr-Einstein condensate(BEC) has very low & even zero kinetic energies. Due to this zero kinetic energies atoms loose their molecular motions & begin to clump together and form condensates named BEC’s. We have to make a note that kinetic energies are directly proportional to absolute temperatures & hence BEC’s also would form & exist at extremely low temperatures.
  6. 6. GASES  As we all know the properties of gases or the gas mixtures .. The formost property is DIFFUSION of GASES  Diffusion is the movement of gases from a region of higher concentration to a region of lower concentration which is exactly opposite to OSMOSIS which is a property of liquids.  Now this diffusion of gases is measured in terms of rates of diffusion.
  7. 7. Rate of Diffusion(r)  The volume of a gas that diffuses in unit time is said to be rate of diffusion (r) of a gas . r=V/t or r1/r2 = V1/V2 * t2/t1 if the two gases have equal volumes then , r1/r2 = t2/t1
  8. 8. EFFUSION  Similar to diffusion , EFFUSION is also a property of gases  Effusion is defined as the movement of gases from a region of higher concentration to that of lower concentration through a small pore.  The best example of effusion are like… 1) Escape of air from balloon 2) Escape of air from punctured cycle tube. 3) Gas leakages from pipes / cylinders
  9. 9. GAS LAWS  A very imp. arena of this chapter is on gas laws.  Here we shall deal with 5 gas laws…. 1) Boyle ‘s law 2) Charles law 3) Avogadros law 4) Grahams law of Diffusion 5) Dalton’s law Lets see one by one in detail……
  10. 10. PV = K Boyle’s law  The pressure of a given mass of gas is inversly proportional to volume at constant temperature. or
  11. 11.  A graph drawn for Boyles law is shown as Pressure vs Volume P V
  12. 12.  If a graph of boyles law is drawn between P vs 1/V , That is represented as P 1/V
  13. 13.  Similarly if a graph is drawn among PV vs P is given as PV P
  14. 14. Charles laws  Statement 1 Charles law -1 1 states that , at constant pressure for every one degree rise in temperature , the volume of a given mass of gas changes by 1/273 of its volume at ‘0’ degrees centigrade. Vt= V0 1+ t/273
  15. 15. Charles law-1 graph  A graph plotted for statement 1 of charles law is shown as V m v0 0 T
  16. 16. Statement - 2  It states that at constant volume , pressure of a given mass of gas is directly proportional to temperature or At constant pressure, volume of a given mass of gas is directly proportional to temperature . V T or P T V=KT P=KT V1/V2=T1/T2 P1/P2=T1/T2
  17. 17. Graphical representation  The graphs drawn for charles law 1 & 2 are given as V3 P3 V2 P2 P1 V1 V P T T
  18. 18. AVOGADRO’S law  Equal volumes of all gases contain equal number of molecules under similar conditions of temperature and pressure. & or or V n V=nK V/n = K V1/n1=V2/n2 V1n2=V2n1
  19. 19. IDEAL GAS EQUATION From the 3 gas laws , studied till now … ideal gas equation can be derived as follows PV=K ……… eq 1 P=KT ……... eq 2 V= nK ………. eq 3 From 1,2 & 3 PV=nKT Replacing constant K, with Universal gas Constant we get PV=nRT
  20. 20. Values of ‘R’ NUMERICAL VALUE UNITS 8.314 Joules 0.08206 L.atm 1.987 Calories 62.36 L.torr 82.1 atm.cc
  21. 21. GRAHAMS LAW OF DIFFUSION  Grahams law of diffusion states that the rate of diffusion of a gas is inversly proportional to the squareroot of density or molecular weight.
  22. 22. DALTONS LAW  It states that , at constant temperature the total pressure of a gas in a gaseous mixture is the sum of partial pressures of the gases. P= p1+p2+p3+…….. At const. ‘T’ ; the partial pressure of a gas is directly proportional to its molefraction (
  23. 23. Kinetic gas Equation  The kinetic gas equation is given as PV=1/3 mnc2
  24. 24. Types of velocities  Gas molecules exhibit with three different kinds of velocities … 1) Average velocity ( C ) 2) Most probable velocity ( C p ) 3) Root meansquare velocity ( C rms )
  25. 25. Ratio of velocities The ratio of C p , C & Crms can be given as 1:1.128 : 1.223
  26. 26. INTERMOLECULAR FORCES vs THERMAL ENERGY  Inter molecular forces are forces which mediate interraction between molecules; be it forces of attraction or forces of repulsion.  These intermolecular forces of attraction are cheifly studied as hydrogen bonding , dipole forces of attraction.  Thermal energy is the average kinetic energy of the molecules of a substance. Thermal energy is a very key factor for the liquifaction of gases.
  27. 27.  Physical state of a substance always depends on the extent of intermolecular forces & thermal energy.
  28. 28. REAL GAS vs IDEAL GAS  Gases which follow ideal gas equation i.e PV=nRT are said to be ideal gases & Gases which donot follow ideal gas equation are said be real gases. And in general , all gases are real & no gas is ideal. The reason behind real behaviour of gases are 1) Molecules of a gas donot exhibit any forces of attraction among them. 2) Volume of gas occupied is negligibly small wrt space occupied by the gas.
  29. 29. GRAPHICAL NOTE CO CH4 H2 He PV P Real gas ideal gas Ideal gas P V
  30. 30. LIQUIFACTION OF GASES  Ideal gases cannot be liquified.it is only a real gas that can be liquified.  Gases can be liquified on cooling below their boiling points.But if the gas to be liquified is having a very low boiling point , then it cannot be liquified by cooling furthur. Hence an another technique called JOULE-THOMPSON EFFECT is to be used. Principle behind this technique is cooling of gases by expansion from high pressure to low pressure.
  31. 31.  There are 2 key points to achieve liquifaction of gases 1) Critical temperature ( Ct ) 2) Critical pressure ( C p ) The highest temperature at which liquifaction of gases occurs first is Ct & the pressure required to liquify a gas at its critical temperature is its Cp.
  32. 32. THANKYOU